1. Field of the Invention
The present invention relates generally to excavation work and subterranean tunneling, and more particularly to a method and apparatus for cementitious grouting of the annular cavity between a tunnel bore and the segmented liner which is installed behind a tunnel boring machine.
2. Background
In modern construction, large diameter tunnels are commonly excavated by means of a tunnel boring machine (TBM).
The tunnel boring machine is not itself a part of the present invention, but its basic components and operation will be described here to give the reader a better understanding of the invention. An exemplary TBM 10 is shown in FIG. 1, as this is engaged in boring through a subterranean formation 12. A large rotating cutter head 14 having a series of cutter teeth 16 on its forward face is located at the forward end of the TBM. The machinery for rotating the cutter head and the associated controls (not shown) are housed within a cylindrical steel shield 20. Rubble 22 (see FIG. 2) which is removed from the rock face by the cutter head is picked up and transported by screw lift 24, from which the material is discharged onto a belt conveyer 26 for removal through the excavated bore.
A tunnel liner 30 is normally installed in the tunnel bore 32 behind the TBM. In most large diameter excavations the liner is of the segmental type, as is shown in FIGS. 1 and 2, wherein the liner is formed of a series of arcuate segments 34 which are assembled inside the telescoping tail shield 36 of the TBM. Typically, the liner segments 34 are transported to the installation site on rail cars 38, and are assembled by means of a traveling hoist 40. The latter is provided with an arm mechanism 42 by which the liner segments 34 are placed to form a circular segment of the cylindrical liner, the segments 34 typically being held in place by bolts, interlocking lugs, or other features.
The tunnel liner 30, in addition to providing a containment/support structure and preventing the collapse of material into the interior of the tunnel, provides a reaction point against which the TBM 10 "pushes off" to effect its forward motion; hydraulic jack mechanisms (not shown) mounted within the TBM thrust against the forwardmost liner segments, in the directions indicated by arrows 44, as the machine works its way through the subterranean formation. After the machine has moved forward to a certain point, the jacks and telescoping tail shield 36 are withdrawn forwardly to permit the installation of another ring of liner segments.
Because the TBM "pushes off" from the ring of liner segments, it is essential that the annular gap 46 exterior to the segments be filled with a supporting material, lest the segments buckle outwardly and become displaced in response to the compressive forces which are exerted against the forward edge of the ring. As is illustrated in FIGS. 4 and 5, this has been done in the prior art by filling the annular gap with gravel 48 or other unconsolidated material. Typically, this is done by bringing a gravel cart (not shown) into the tunnel and then blowing the gravel into the annular cavity using compressed air, as through the hose 50 which is shown in FIG. 4. This approach, however, has exhibited numerous deficiencies in practice. Firstly, blowing the gravel into place is a very slow and labor-intensive operation; the operator personnel must move the hose 50 around to place the gravel, and the material is difficult to work with. As a result, the gravel car must remain in place for an extended period, blocking the forward end of the tracks and preventing the delivery of additional liner segments. This, in turn, prevents forward progress of the TBM during this period; because the hourly cost of operating the TBM and its supporting systems is exceedingly high, these delays add greatly to the total cost of the tunneling operation.
Another problem with using gravel or other loose or unconsolidating material to fill the annulus 48 is that this tends to cascade or spill down on the sides of the liner segments leaving unfilled gaps at the cown of the liner and spilling into the interior of the TBM shield, as indicated at area 52 in FIG. 4, from which it must be removed or else it may impair the operation of the machine. Moreover, in order to complete the installation, it is necessary to follow the placement of the gravel by the injection or "squeezing" of cement grout through ports 53 in the liner segments, adding to the overall cost of the operation.
Some attempts have been made to use conventional cement grouts to fill the annulus, in place of gravel. These attempts have proven wholly unsuccessful, because the fluid grout is simply too "runny" and flows down along the liner and spills out into the interior of the shield, in a manner similar to the gravel shown in FIG. 4 but only worse. Moreover, if a conventional cement grout begins to set up in the gap 54 between the liner and the tail shield 36, the material will stick to the liner and shield, making it impossible to retract the latter. The gravel avoids this problem because of its unconsolidated nature, but at the cost of the other problems described above.
Polyurethane foam grouts are quick setting and therefore might eliminate some of the problems noted above. However, the toxic fumes, high flammability and high exothermic temperatures which are associated with polyurethane grouts present unacceptable safety hazards in a closed, subterranean environment.
Accordingly, there exists a need for a method and apparatus for filling the annular cavity between a tunnel liner and the tunnel bore which is expeditious and does not require excessive manpower to accomplish. Moreover, there is a need for such a method and apparatus which obviates the problem of the fill material spilling into the interior of the tunnel boring machine and leaving gaps at the crown of the liner. Still further, there is a need for such a method and apparatus which utilizes a fill material which is both economical and acceptable from a safety standpoint.